Fig. 3. Transplantation of in vitro grown micro-tissues: Early cell retention. The fraction of cells remaining after direct intra-myocardial injection was measured by real time PCR. Detection of male cells ("SRY") indicates the fraction of MSCs and ES-CMs together; detection of the puromycin-acetyltransferase-transgene ("CM") specifically indicates the fraction of ES-CMs that was retained in the tissue 24 or 48 hours after transplantation. The cell number initially injected was set as 100% using a control where cells were directly added to an explanted heart in a reaction tube and processed for DNA extraction.